This invention relates to tube plugs and more particularly to apparatus for plugging heat exchanger tubes.
In tube-type heat exchangers, a first fluid flows through the tubes of the heat exchanger while a second fluid surrounds the outside of the tubes such that heat exchange occurs between the two fluids. Occasionally, one of the tubes can become defective such that a leak either is impending or occurs therein which allows the two fluids to mingle. When this occurs, is is sometimes necessary to plug the tube so that the fluid does not flow through the tube thereby preventing leakage from the tube.
In nuclear reactor power plants, the tube-type heat exchangers are commonly referred to as steam generators. When a defect occurs in the tubes of a nuclear steam generator that allows the coolant in the tubes to mingle with the coolant outside of the tubes, a more significant problem arises. Not only does this situation create an ineffective heat exchanger, but it also creates a radioactive contamination problem. Since the fluid flowing in the tubes of a nuclear steam generator is generally radioactive, it is important that it not be allowed to leak from the tubes and contaminate the fluid surrounding the tubes. Therefore, when a leak occurs in a nuclear steam generator heat exchange tube, the heat exchange tube is plugged so that the coolant is not permitted to flow through the tube. This prevents contamination of the fluid surrounding the tubes.
There are several kinds of plugs that may be used to plug the heat exchange tubes. One such device used to plug heat exchange tubes in nuclear steam generators is an explosive plugging device. With the explosive plugging devices, a metal plug is inserted in the heat exchange tube with an explosive contained within the plug. When the explosive is detonated, the plug is forced into close contact with the inside of the tube, thus blocking flow through the tube. One problem associated with explosive plugging is that should it become necessary to replace the defective tube or defective plug, the explosive plug must be removed by machining methods which is a time consuming procedure.
There are also several kinds of mechanical plugs that can be used to plug heat exchange tubes which do not use explosives. However, these mechanical plugs suffer from defects such as not being as leak tight as necessary, difficult to remove from a tube, difficult to install in a tube, or require assembly in the field. Since tube plugs to be used in a nuclear reactor environment must be easily installable, leak tight, and easily removable, the mechanical plugs known in the prior art are generally not acceptable for use in nuclear steam generators. Therefore, what is needed is a mechanical plug that is capable of being quickly and easily installed in a heat exchange tube of a nuclear steam generator for preventing the flow of reactor coolant therethrough.